detectSURFFeatures gives empty object back

if true
   Points = detectSURFFeatures(test)
   imshow(test);
   hold on;
   plot(selectStrongest(Points, 100))
end

I used the code bellow to extract Features of my 2-D grayscale image "test" ( double or uint16) but the function detectSURFFeatures gives me an empty object back so when i want to plot i become this error

 if true 
        to the || and && operators must be convertible to logical scalar values.

error in vision.internal.FeaturePoints/plot (line 152)
           if k==1 && ~wasHeld

error in SURFPoints/plot (line 172)
       h = [e-mail](this, ...    

end
Any help please ?